The present invention relates to document processing equipment, and more particularly to a document transport apparatus at a document processing station for providing accurate processing.
Printing on documents using non-fully-formed devices requires accurate knowledge of the motion of the document in order to place dots or spray lines on the document with sufficient accuracy for machine reading. Typically, motors and synchronous belts are used to impart motion to document drive rollers. These motors and belts have cogging forces which can sometimes cause short term speed fluctuations. Because characters or symbols to be printed are typically small (about xe2x85x9 inch or smaller), such short term speed fluctuations can cause inaccurate character placement. This inaccurate placement of the ink on the document makes the character or symbol impossible to machine read.
Printer accuracy can be improved by reducing the cogging forces of the drive rollers. Conventional systems attempt to reduce the cogging forces by providing extremely high precision motors and motion transmission devices which are expensive. Other systems use flywheels to minimize short term speed fluctuations caused by cogging or other pulsing type forces.
In addition, many other types of document transports allow approximately 0.1 inch of document movement perpendicular to the transport direction. As such, conventional document transport systems used in conjunction with non-fully-formed character printers may allow the document to slip with respect to drive rollers because they do not enable a firm grip. Speed regulation is inadequate unless extra flywheels are added, which add to the space issues, cost issues and complexity of the document transport.
In general, a flywheel is a device for storing energy or momentum in a rotating mass. Flywheels are usually a heavy wheel which may be any shape, such as disk or saucer, and are typically symmetric. Flywheels are used for a variety of purposes. One commonly known mechanical purpose of flywheels is to moderate speed variations in an engine. The flywheel uses its inertia to even out quick power outbursts by a power supply or sudden loads on a system.
As such, it is desirable to provide a document transport for providing speed regulation for documents that are to have characters or other machine readable symbols printed on them by non-fully-formed character or symbol printing devices, such as ink-jet printers, or thermal or impact dot matrix printers, and the like.
The present invention provides document drive rollers that are of relatively large moment of inertia to minimize speed fluctuations and are simultaneously arranged so as to enable a firm grip of the document while being printed.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.